Where to find the units setting in AutoCAD

Open AutoCAD and go to the process Menu — the red "A" icon in the top left corner. Click it, then select Drawing Utilities, then Units. A dialog box titled "Drawing Units" will open. This is where you control whether your drawing measures in inches, millimeters, feet, centimeters, or other units.

If you are already in a drawing and want a faster route, type UNITS directly into the command line at the bottom of the screen and press Enter. The same dialog box appears. Either method takes you to the same place.

The dialog shows your current unit type in a dropdown menu. Next to it you will see options for precision — how many decimal places AutoCAD displays — and the angle format. You change the unit type by clicking the dropdown and selecting from the list.

Key Takeaways

  • The units setting controls what measurement system your drawing uses, and you reach it through process Menu > Drawing Utilities > Units or by typing UNITS at the command line.
  • Changing units in an existing drawing does not rescale your geometry — a line that was 10 inches long stays 10 units long, but now those units are called millimeters instead.
  • If you need to rescale existing geometry when you change units, use the SCALE command after changing the unit type, not the units dialog itself.
  • Set your units before you start drawing whenever possible, because changing them mid-project requires you to manually rescale or redraw affected geometry.

Understanding what happens when you change units

This is the part that confuses most people. Changing the unit type does not automatically resize your drawing. If you drew a line 10 inches long, then changed the units from inches to millimeters, that line is now 10 millimeters long — which is much smaller. The numbers stay the same; only the label changes.

AutoCAD treats the change as a relabeling, not a conversion. Your geometry does not move or resize on its own. If you want a line that was 10 inches to become 10 millimeters in actual size, you have to manually rescale it using the SCALE command after you change the units.

This is why setting units before you start drawing matters. If you plan to work in millimeters, set that from the beginning. If you inherit a drawing in the wrong units, you will need to decide whether to rescale everything or accept that the numbers mean something different than they did before.

How to rescale a drawing after changing units

If you have already drawn in inches and now need everything to be in millimeters at the correct physical size, use the SCALE command. Type SCALE at the command line and press Enter. AutoCAD will ask you to select objects — click and drag to select all the geometry you want to rescale, or type ALL and press Enter to select everything in the drawing.

After you select the objects, AutoCAD asks for a base point. This is the point that stays fixed while everything else scales around it. Usually you can just press Enter to accept the default, or click a corner of your drawing.

Then AutoCAD asks for a scale factor. This is the number you multiply by. If you drew in inches and need to convert to millimeters, the scale factor is 25.4 (because one inch equals 25.4 millimeters). Type 25.4 and press Enter. Your entire drawing rescales, and the numbers now represent millimeters at the correct size.

Setting precision and angle format

The Drawing Units dialog also controls how many decimal places AutoCAD shows when you measure or dimension. The Precision dropdown lets you choose — common options are 0.00 (two decimal places), 0.000 (three decimal places), or 0 (whole numbers only).

Higher precision means AutoCAD displays more decimal places, which is useful for detailed mechanical drawings. Lower precision makes the drawing cleaner and easier to read if you are working at a larger scale, like architectural plans. Choose the precision that matches how accurate your drawing needs to be.

The Angle section works the same way. You can measure angles in degrees, radians, gradians, or surveyor's notation. Most drawings use degrees, which is the default. You also set how many decimal places angles display — usually 0.00 degrees is enough.

Common unit types and when to use them

AutoCAD offers several unit systems. Decimal is the most common — it treats your units as generic numbers, and you decide what they represent (inches, millimeters, feet, whatever). Architectural displays measurements in feet and inches together, like 12'-6" — useful for building plans. Engineering shows feet and decimal inches, like 12.5 feet.

Fractional displays inches as fractions (1/2", 1/4", 1/8") instead of decimals, which is common in woodworking and construction drawings. Scientific uses exponential notation and is rarely used outside specialized fields. Most people start with Decimal and stick with it unless a specific industry standard requires something else.

The unit type you choose affects how dimensions and measurements display, but it does not change how AutoCAD stores the numbers internally. You can always change it later — just remember that existing geometry will not rescale unless you use the SCALE command.

Why your units might not be changing

If you change the units in the Drawing Units dialog and nothing appears to happen, check whether you are looking at a block or an external reference. Blocks and xrefs have their own unit settings that override the drawing units. You may need to edit the block separately or reload the xref.

Another common issue: you changed the units, but your drawing still looks the same size on screen. This is normal. The drawing itself did not rescale — only the label changed. Zoom out or use View > Zoom > Extents to see the whole drawing and confirm the change took effect.

If you are working in a template that was set up in different units, the template's units take priority. Create a new blank drawing or check the template settings if the units keep reverting.

Setting a default unit for new drawings

If you always work in millimeters but AutoCAD keeps defaulting to inches, you can change the template. Go to process Menu > New, and instead of selecting a blank drawing, look for a template file that matches your needs. If none exists, create a blank drawing, set the units to millimeters, then save it as a template in your AutoCAD Templates folder.

The next time you start a new drawing, you can select your custom template and it will open with millimeters already set. This saves you from changing units every single time you start a project.

Frequently Asked Questions

If I change units, do my dimensions change too?

No. Dimensions are tied to the geometry they measure, not to the unit system. If a line is 10 inches and you change units to millimeters, the dimension still reads 10 — now in millimeters. The dimension text does not automatically convert. You would need to rescale the geometry with the SCALE command to make the dimension read 254 (which is 10 inches in millimeters).

Can I have different units in different parts of the same drawing?

No. AutoCAD uses one unit system per drawing. If you need to mix units — say, a building in feet and a detail in millimeters — you have to work in one unit and convert manually, or use separate drawings and link them together.

What happens if I open a drawing that was made in different units?

AutoCAD opens it in whatever units it was saved in. If it was drawn in inches and you work in millimeters, the geometry will be the wrong size. You can rescale it with the SCALE command, or change the units and rescale to match your system.

Does changing units affect file size or performance?

No. The unit system is just a label. Changing it does not make the file larger, smaller, or slower. It only changes how AutoCAD displays and interprets the numbers you see on screen.

Can I use custom units that AutoCAD does not list?

Not directly. AutoCAD's unit types are fixed. If you need a custom measurement system, work in decimal units and document what each unit represents — for example, "1 unit = 1 centimeter" — then share that note with anyone else who opens the drawing.